[Bug dynamic-link/15533] New: LD_AUDIT introduces an avoidable performance degradation

["amonakov at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=15533

            Bug ID: 15533
           Summary: LD_AUDIT introduces an avoidable performance
                    degradation
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: amonakov at gmail dot com

Created attachment 7044
  --> http://sourceware.org/bugzilla/attachment.cgi?id=7044&action=edit
testcase

Introducing an audit library currently force-enables instrumenting for
profiling in the dynamic linker (as if LD_AUDIT implied LD_PROFILE).  However,
this is not necessary if the audit library does not provide la_plt{enter,exit}
symbols.

Attached testcase demonstrates the performance hit:

$ make test
time ./main
0.47user 0.00system 0:00.48elapsed 99%CPU (0avgtext+0avgdata 1984maxresident)k
0inputs+0outputs (0major+170minor)pagefaults 0swaps
time env LD_AUDIT=./libaudit.so ./main
8.96user 0.00system 0:08.97elapsed 99%CPU (0avgtext+0avgdata 3264maxresident)k
0inputs+0outputs (0major+442minor)pagefaults 0swaps

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